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COVID-19 vaccines help our bodies to develop immunity against the virus. Different types of vaccines work in different ways to offer protection. With all the types of vaccines, the body is left with a supply of “memory” T-lymphocytes cells as well as B-lymphocytes cells which make sure to remember that virus and fight against it in future. Antibodies are produced from B-lymphocyte whereas T-cell helps in attacking the virus.

What is Antibody?

Antibodies, like IgM and IgG, are the proteins which are produced in response to infection due to micro-organisms like bacteria, virus etc. in the individuals and help to fight with them. Immune system on the other hand, recognise these micro-organisms by killing them, thus help in eliminating the organisms. As the infections frequency increases, immune system become trained to focus its attack by making specific antibodies.

Why the antibody test is important in coronavirus disease?

A Covid-19 antibody test, also called as serology test, is a blood test, done to understand the presence of antibodies against the Covid-19 infection. Although this test does not detect the virus directly but help to identify if the individual has infected previously from the virus. To detect if an individual has an active coronavirus infection or not, some other diagnostic tests are available like

• Molecular (RT-PCR) tests, which detect the virus' genetic material

• Antigen tests that detect specific proteins on the surface of the virus

The antibody tests for SARS-CoV-2 can be qualitative, which means that it only provides  a ‘positive’, ‘negative’ or ‘indeterminate/equivocal’ result or can be semi-quantitative or quantitative, where the reported value indicates a general level of antibodies in the blood. However, what level of antibodies are necessary for protection against re-infection and how long they last are uncertain.

Exactly how long these antibodies may remain in the body to protect against infection?

Current researchers are not sure about the duration of the immunity i.e. how long the antibodies remain in blood of the Covid-19 patients but data suggest that antibodies IgM develop after first week of COVID-19 infection, while IgG antibodies become detectable sometime beyond 14 days of infection.

Data published in ‘Nature journal’ shows that there was a rapid decrease of antibody levels occurs within 2 or 3 months of infection, whereby other research also shows that these antibodies had a half-life of 73 days, that is, half of them would be gone after that much time.

A study on 175 patients recovered from mild Covid-19 shows wide variation in the levels of antibodies against the novel coronavirus, ranging from very high levels in 2 patients to undetectable levels in 10 with the same duration of illness – published in JAMA Internal Medicine.

Few other studies also mentioned that the level of antibody are specific in Covid-19 patients, following some variations between those who have severe disease (higher levels of antibodies) and those with milder disease or asymptomatic infection (lower levels of antibodies) like, the level of antibody IgM were observed slightly higher in deceased patients than recovered patients, but IgG levels in these groups did not significantly differ. Several studies has found level of antibodies produced in the individual of as mentioned below.

Can Covid-19 patients after development of antibodies or vaccination, re-infect or transmit infection?

Role of antibodies in neutralising infection and preventing from re-infection against Covid-19 has become important to understand the duration of immunity, however the presence of antibodies does not guarantee the immunity.

According to a small Israeli survey, out of 102 medical staff who had received two doses of the vaccine, only two had developed "low" amounts of antibodies. The other 98% were investigated to have more amount of antibodies compared to people who had been infected with Covid-19. More recently, the Israeli Ministry of Health (MoH) looked at the health records of a million people in the country, and found that only 317 people out of 715,425 tested positive for the coronavirus infection after one week of being fully vaccinated.

Re-infection by covid-19 after four months, was reported in a 33-year-old man from Hong Kong but no symptoms was seen, clearly showed that immunity was produced in the body at the time of first infection, which prevented from the occurrence of any symptoms after re-infection by Coronavirus.

No evidence found yet, that Covid vaccines completely stop people from being infected but the Covid antibodies produced against Covid-19 infection, can protect individual from getting severe symptoms after re-infection. Many  research says that the immunity develop after first infection can fight a second infection and show mild symptoms after re-infection but experts says that more data is required to confirm how long immunity against Coronavirus lasts and does it prevents re-infection.